You can change your account information using Personal Profile -> 'Edit Profile' option from within the User Control Panel. If you want to change your Password there is an extra Page (Change Password) for that in the User Control Panel, where you can set a new Password.

Edit Profile Page

This page allows you to set a number of required and optional details, some of which will be displayed on your public profile. With the exception of your e-mail address, do not enter information that you do not wish to be publicly viewable.